My two pence worth OP is that I think it would be best to put less stock in the wishes and comments of your DD's tutors- what are her grades like otherwise aside from her art? The push could be towards it because they on paper see a better grade success rate for her there. Teachers have statistics to meet also. That aside it needs to be up to her.
I don't think the fact she has artistic leanings and talent is in dispute so much as the fact that so do an awful lot of other individuals. From a personal perspective (I did a careers based art qualification, art a level and degree, and the industry has changed a lot/was changing back then. I know very few peers who make any substantial money from fine art, the most successful of them are those who create digital art, graphic art or animation based stuff. If she is serious about it as a paying career she will realistically need that skill set and full competency in the up to date digital programmes to secure a decent post grad job or internship.
As others have pointed out she will also need strong networking skills, ideally existing connections and absolutely money to fund herself. It's a tight knit industry in my experience and has more talent than salaried jobs.
She could teach art? Or explore the careers relating to it such as museum management or art therapy perhaps (still very hard to get into). There is a lot to be said for killing the passion by making it a career also, she will need a huge portfolio and distinctive style- however well graded an a level piece is, it has no bearing on what will commercially sell unfortunately.
I agree with previous posters who advise her to do other a levels, then do a foundation year if she wants to see if it is for her. I'd encourage her to produce a portfolio unrelated to her school or college assigned topics, develop her style, try to get her to reach out to exhibit locally enter competitions etc in anything going and see how she finds that. It would provide decent perspective as to whether it could work as a career.